Stereoselective synthesis of substituted 1,2-annulated sugars by domino double-Michael addition reaction.

A simple, highly stereoselective one-pot methodology for the synthesis of novel 1,2-annulated sugars comprising of oxa-oxa and oxa-carbasugar fused skeletons from 2-nitrogalactal and a sugar-derived enone, obtained from 2-formylgalactal, promoted by KOtBu and CH3ONa respectively is described. Both processes rely on a domino double-Michael addition reaction resulting in the formation of three stereocenters in a single pot, including a quaternary center.